1. Field of the Invention:
The present invention relates to adjusting the fuel pressure supplied to an internal combustion engine by controlling a fuel pump.
2. Description of Related Art:
A returnless piping structure having no fuel return to the fuel tank for surplus fuel fed to an engine fuel injector has been employed to simplify the fuel conduit and thus realize a reduction in size and cost. In this case, as described in Japanese Patent Application Laid-open No. 6-147047, a fuel pressure sensor detects piping system pressure and provide a voltage to a built-in fuel pump motor that is controlled through a feedback loop so that fuel pressure matches the target fuel pressure.
However, in this system, since the amount of fuel discharged from the fuel pump increases after the amount of fuel consumed in the engine increases, for example, during a transition period (engine acceleration) where the amount of fuel injected from the injector increases quickly, fuel pressure is temporarily lowered due to delay in both control response and fuel transfer. On the contrary, when the amount of fuel discharged from the fuel pump is reduced after the amount of fuel consumed in the engine is decreased during a transition period (engine deceleration) where the amount of fuel injection reduces quickly, fuel pressure is temporarily increased due to delayed control responses. Such variation of fuel pressure causes deviation of the air-fuel ratio supplied to the internal combustion engine and thus also results in deterioration of exhaust emission and drivability.
In order to avoid such drawbacks, it is proposed that such delay of transition responses be compensated by detecting the rate of transitional variation of the requested amount of fuel injection and then calculating with mapped data stored in a memory an appropriate compensating value depending on such rate of transitional variation.
However, the system has a disadvantage in that the arithmetic operations required are rather complicated and a large amount of memory capacity is required because it is required, as explained above, to detect a rate of transitional variation of the requested amount of fuel injection and to calculate with the mapped data the compensating value depending on such a rate of transitional variation.